HR: 16:15h
AN: GP24A-02    [Abstracts]
TI: A Data-Model Comparison of Geomagnetic Field Evolution in Fennoscandia since 7000 cal BP
AU: * Snowball, I
EM: ian.snowball@geol.lu.se
AF: Geobiosphere Science Centre, Lund University Solvegatan 12, Lund, 223 62 Sweden
AU: Zill‚n, L
EM: lovisa.zillen@geol.lu.se
AF: Geobiosphere Science Centre, Lund University Solvegatan 12, Lund, 223 62 Sweden
AU: Sandgren, P
EM: per.sandgren@geol.lu.se
AF: Geobiosphere Science Centre, Lund University Solvegatan 12, Lund, 223 62 Sweden
AU: Stanton, T
EM: tania.stanton@geol.lu.se
AF: Geobiosphere Science Centre, Lund University Solvegatan 12, Lund, 223 62 Sweden
AB: A recently published geomagnetic field model (CALS7K.2, Korte and Constable, 2005) predicts inclination, declination and intensity values for the last 7000 years at any point on the Earth's surface. We compare this model's output for the Fennoscandian region to a series of seven high-resolution and independently dated records of geomagnetic field evolution derived from lake sediments. None of these records were used to constrain the constructed model, so differences between the modeled time series and the empirical data may indicate model deficiencies or poor reconstructions. Six of the sediment sequences have chronologies based on the counting of annual laminations (varves). Two of these varve chronologies are validated by radiocarbon dating and tephrochronology. The chronology of the seventh site is based on secular variation correlation, but with validation by radiocarbon dating. The seven records contain all of the directional features that were first reconstructed in a study of lake sediments located in the United Kingdom (Turner and Thompson, 1981) although discrepancies of the ages of curvature maximums can differ by as much as 400 years. We find that this difference has no relationship to the longitudes of the sites, which suggests that dating errors could be responsible instead of significant westwards drift of geomagnetic field features. As implied by other palaeomagnetic studies in high-latitudes on the northern hemisphere the most rapid change in field direction occurred at c. 3000 cal BP and was dominated by a change in declination. This feature is predicted by the CALS3K.1 model, but not the CALS7K.2 model, while an older predicted declination feature at c. 4000 cal BP is not indicated by our data compilation. Inclination differences are also greatest at c. 3000 cal BP. In general, the differences between predicted directions and our reconstructions increase further back in time. It is notable that the general trends in the relative paleointensity records obtained from the seven sites agree well with the modeled intensities. In fact, the overall differences are not significantly greater if the local RPI records are compared to the model's prediction of global dipole moment. This implies that paleointensity can form the basis of intra-hemispheric correlation if it can be reconstructed accurately.
DE: 1521 Paleointensity
DE: 1522 Paleomagnetic secular variation
DE: 1560 Time variations: secular and longer
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005